Different hardness would definitely make things sound different. Back when I had a Rega, I used squash balls (don't know if there's an equivalent in North America) under the Ikea butchers block as a suspension. There war various hardness for squash balls so tweaking with placement and mix of hardness was a good month's entertainment. I used rubber ring gaskets used in plumbing to make sure the balls didn't roll around.
For a long time there were people using Raquet balls cut criss cross (that would absorrb sound and prevent the balls from rolling) that were placed under granite slabs or butcher block for turntable isolation.
Rich